One pipe laying apparatus used as an earth-retaining or sheathing apparatus for open cut works includes an approximately box-type frame in the whole form. This known apparatus involves a pair of side plates facing each other at a horizontal interval; a supporting frame attached to the side plates; and a plurality of jacks for advancing the supporting frame. In this known apparatus, earth pressure is received by the side plates, and a reaction force is received by a pipe which has been already placed within a channel (designated as a "pipe already installed" hereafter).
This known apparatus is advanced in the channel formed in the ground, while the channel is extended by a known machine, such as a back hoe. After the channel is extended by a required length, a new pipe is placed within the channel and connected to the pipe already installed. Specifically, an excavation and advance operation for excavating the ground while advancing the laying apparatus and a placement and connection operation for placing a new pipe in the channel and connecting the new pipe to the pipe already installed are performed alternately.
This known laying apparatus and methods for laying a pipe thereby, however, are based on loading the reaction force generated in advancing the apparatus on the pipe already installed. The excavation and advance operation is therefore not performed simultaneously with the placement and connection operation. A buffer material for preventing breakage of the end surfaces of the pipe already installed should be placed between the pipe already installed and the jack when the prior art apparatus is used. Further, a large-sized jack having a stroke larger than the length of the pipe to be installed should be used with this prior art device.